The disclosure of Japanese Patent Application No. 2000-375380 filed on Dec. 11, 2000 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of Invention
The invention relates to hydrogen gas generating systems for generating hydrogen gas by reforming raw material. This invention also relates to methods for stopping operation of fuel cell systems, which use the hydrogen gas generating systems.
2. Description of Related Art
Fuel cells generally generate electricity by an electrochemical reaction between hydrogen gas and oxygen in the air. Hydrogen gas is generated, for example, by reforming raw material. Generally, natural gas, gasoline or other hydrocarbon, alcohol, ethyl, aldehyde, or the like, may be used as the raw material. Reformed gas containing hydrogen and carbon monoxide is generated by reforming these raw materials. Due, however, to the fact that carbon monoxide is a toxic substance that poisons the electrodes of fuel cells, reformed gas is usually supplied to the fuel cell after being treated, so that only the carbon monoxide is selectively oxidized.
When stopping operation of a fuel cell system, which includes a unit for generating reformed gas (hereinafter referred to as hydrogen gas) by reforming and a fuel cell, it is necessary to discharge the flammable gas containing carbon, etc., deposited during reforming, as well as toxic gas from the system. This discharge prevents against adverse effects, such as the harmful effects from these gasses leaking from the system and the poisoning of the electrodes of the fuel cell caused by these gasses, from occurring within the system. As art related to the above-mentioned object, there has been art in which, when stopping operation of a fuel cell system, inert gas is supplied into the system, so as to purge residual flammable material inside the system.
With this type of system, however, it is necessary to store an inert gas for purging in a separate tank beforehand. Because the inert gas is unable to be used for either reforming and generating electricity, storing the inert gas only for purging requires a large waste of both storage space and operating costs.
On the other hand, no other gas than inert gas appeared suitable for purging the residual flammable material. For example, if a gas containing oxygen is supplied to the system, the flammable component in the residual flammable material within the system reacts with the oxygen to generate heat, and this heat may have an effect on the system. And if a gas containing steam is supplied, condensation is generated in the system after purging, which not only makes restarting of the system difficult, but may also decrease the catalytic performance of the fuel cell. Moreover, if there is condensation at a low temperature, there is the possibility of the system freezing inside. In consideration of these adverse effects, it was necessary to use inert gas as a purge gas despite the waste in storage space and costs.
In order to solve the foregoing problems, it is an object of the invention to provide an invention for purging residual flammable material within a system without relying on inert gas.
In order to solve the foregoing problems, hydrogen gas generating systems according to the invention generate hydrogen gas by reforming a raw material, and purge during stopping of the operation of the system using steam and air, which are gasses that are used also during operation of the system. Each of the various problems exemplified above are solved by controlling the supply of these gasses.
Accordingly, methods for stopping operation of hydrogen gas generating systems that generate hydrogen gas by reforming a raw material according to exemplary embodiments of the invention, comprise the step of purging a residual flammable material by supplying air into the hydrogen gas generating system when it is determined that there is no effect on the hydrogen gas generating system from heat generated by a reaction of residual flammable material within the hydrogen gas generating system and oxygen.
Methods according to the invention for stopping operation of fuel cell systems comprising a hydrogen gas generating system, which generates hydrogen gas by reforming a raw material and a fuel cell, which generates electricity using the generated hydrogen, comprise the step of purging a residual flammable material by supplying air when it is determined that there will be no effect on the hydrogen gas generating system and the fuel cell from heat generated by a reaction between a residual flammable material within the hydrogen gas generating system and the fuel cell and oxygen.
Hydrogen gas generating systems according to the invention for generating hydrogen gas by reforming a raw material, comprise a reforming portion for reforming an air supply portion for supplying air to the reforming portion and a control portion for controlling the air supply portion during a stopping operation, so as to supply air into the reforming portion when it is determined that that there will be no effect on the hydrogen gas generating system from heat generated by a reaction between a residual flammable material within the reforming portion and oxygen.
Fuel cell systems according to the invention comprising a hydrogen gas generating system, which generates hydrogen gas by reforming a raw material and a fuel cell, which generates electricity using the generated hydrogen, comprise a reforming portion for reforming an air supply portion for supplying air to the reforming portion and a control portion for controlling the air supply portion during a stopping operation, so as to supply air into the reforming portion when it is determined that there will be no effect on the hydrogen gas generating system from heat generated by a reaction between a residual flammable material within the reforming portion and oxygen.